Indexer: persist revocation reason and expose it on Attestation type

[Haroldwonder]

Summary

revoke_attestation accepts and emits a revocation reason, and the contract's audit log stores it, but indexer/prisma/schema.prisma's Attestation model has no revocationReason column, so the GraphQL Attestation type can't return it.

Acceptance Criteria

• Add revocationReason column to the Attestation Prisma model via a new migration.
• Revocation event handler populates it.
• Field exposed on the GraphQL Attestation type.

[temisan0x]

@temisan0x has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi Maintainer! I'd love to take on this issue

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[Mirabliss]

@Mirabliss has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello i would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Mirabliss to this issue.

[drips-wave]

Congratulations, @Mirabliss! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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